Automatically variable resistance



June 3, 1941. G. HOLMES ETAL AUTOMATICALLY VARIABLE RESISTANCE Filed July 15, 1938 1 II. a 54147471717474?! v 'r is. I

Sumter! attorney Patented June 3, 1941 2,244,644 AUTOMATICAILY VARIABLE RESISTANCE Gifford 1. Holmes,

Craig, Bobblnadaie,

apoiis-Honeywell Regulator Company,

Minn, a corporation of Delaware sp s,

Minneapolis, and Robert 8.

Minn, assignol'l to Minne- Minne- Appllcatlon Jn1y'15, 1938, Serial No. 219,396

14 Claim.

This invention is directed broadly to a variable resistance, and-more specifically to a resistance which is sealed within an enclosure and varied by means of a device responding to changes in a condition, such as temperature, pressure, humidity. etc., and which is located outside of the enclosure.

One of the most diilicult problems to contend with in the design of an automatically variable resistance is that of a lumpy action between the resistance element and the element which moves across it. It is found. for example, that where a metallic slider is moved by means of a condition responsive element. such as a bellows or bimetallic thermostat. across a coiled resistance wire that there is a tendency, on a uniform change in temperature or pressure. for the slider to remain stationary for a time and then Jump over a few of the cells, then remain stationary for another period after which it will again Jump over a few more of the resistance cells. The effect of this is to reduce the number of positions which the slider can assume in travelling from one end of the resistanceto the other, as well as to reduce the sensitivity of the condition responsive element moving the slider.

It is therefore an obiect of the present invention to design a resistance which is to be varied in accordance with the variation in a condition value wherein the resistance to movement between the resistance and the control member in contact therewith is reduced to a minimum so as to reduce the tendency for a lumpy action between them and also to increase the sensitivity of the condition responsive "element producing the relative movement.

A further object is to provide a variable resistance in which the resistance element is a coiled wire and the element movable with respect thereto is a globule of mercury, fixed with respect to its support.

Another object of the invention is to provide a sealed glass enclosure in which is flexibly mounted a resistance element and to provide further an external force for moving the resistance element with respect to a globuie of mercury within said enclosure.

Another object is to' provide a resistance as set forth in:the preceding paragraph wherein the external force is applied to the resistance by means of a movable magnet.

Another object is to mount the magnet on a carriage which is pivoted on the same axis about which the resistance element swings, and to counter-balance the carriage and the resistance element by an adjustable weight.

Still another. object is to seal the tube with a flexible seal through which the support for the resistance element extends so that it can be swung back and forth with respect to the tube.

A further object is to flexibly mount the resistance element within the tube, weight it so that it will always hang substantially vertically, and then rock the tube back and forth.

These and other objects will readily become apparent as the following specification is read in the light of the accompanyins drawing in which:

- Figure 1 is a front view. partly in elevation and partly in section of one form of our invention;

Figure 2 is a section taken along the lines 2-2 of Figure 1 and looking in the direction of the arrows;

Figure 3 is a detail view of some of the parts looking in the direction of Figure 1, other parts being omitted for the sake of clarity;

Figure 4 is a front view, partly in elevation and partly in section of a second form of our invention; and

Figure 5 is a front view, partly in elevation and partly in section of a third form of our invention.

Referring first to the modification disclosed in Figures 1, 2, and 3 it will be seen that the base ll supports a bracket, generally indicated at l2, by means of the screws II. The bracket l2 comprises a first knife edge II, a ring portion i5, and a second knife edge It all of which are integrally connected. A sealed glass tube H which is of a constant depth from front to back but which is flared at the lower portion in respect to lts,width as shown in Figure l is suitably connected to and supported by the ring it. At thebottom of the glass tube I1 is an indentation as indicated at ll in which is positioned a globule of mercury is. Sealed into the upper end of the tube i1 is a flexible metal strip 2| to which is connected within the tube a supporting arm 22. The arm 22 at its lower end carries a bar magnet 23 and an insulating member 24 which supports in any suitable manner two resistance elements 2! and 20 which are in the form of tightly coiled wires. It will be noted with reference to Figures 1 and '2 that a small portion of each of the resistance elements is in contact with the globule of mercury which electrically connects these portions of the resistances. Resistance element 2! is center tapped by conductor 22 and the conductors" and 20 are connected to opposite ends of the resistance element 25. As the resistances are moved back and forth across the globule of mercury is various portions "of the resistances will be electrically connected together. These resistances while not of the usual form are of the type which may be used in a control circuit such as is disclosed in the application of John E. Haines, Serial No. 38,946. It will be noted in connection with Figure 2 that the con- .ductor 28 is electrically connected to the arm 22 which is in turn electrically connected to the over the knife edges the two legs of the element I are disposed on opposite sides of the tube H.

The lower extremity of each leg is provided with a cutaway portion 40 into which the two legs of the horse shoe magnet 4| are adapted to fit. The horse shoe magnet is connected to the carriage 31 by means of screws 42 and clamps 43. As seen in Figure 2 the bar magnet 23 is located directly between the two legs of the horse shoe magnet and is so arranged that the north and sent poles of the horse shoe magnet are adjacent south and north poles, respectively, of magnet. It might be pointed out here that if desired a soft iron core could be substituted for the bar magnet and satisfactory results obtained. The carriage 31 is preferably made of some nonmagnetic material such as brass so as not to interfere with the passage of magnetic flux through member 23 from the poles of magnet 6 5.

On the upper end of the carriage 31 a. screw threaded stem 45 on which is adjustably threaded a counter weight 48 for the purpose or. counter balancing the carriage 31, the horse shoe magnet the arm 22, and the bar magnet 23. Elton-s 41 and 48 are provided at the lower of ti base in the path of movement of the ho magnet 4| to limit the extent of rotati carriage 31 about its knife edges M and 41 and 48 are outside the normal magnet 4| and serve merely to protect the instrument from tipping too far in the event the counter weight 45 is placed in such position that it will tend to over balance the carriage 31, magnet 4|, magnet 23, and support 22.

Adiustably mounted on pin 50 which is suitably secured to the base H is an arm which carries at its end a coiled bimetallic thermostat 52 which on expansion and contraction is adapted to move an arm 53 to which it is suitably connected. The upper end of the arm 53 is adapted to carry one end of a coiled tension spring 54, the other end of which engages in the hole 55 in the upper end of the carriage 31, as viewed in Figure 2. The arm 53 and carriage 31 are provided with indentations 51 and 58; respectively, in which the opposite ends of a connecting rod 59 are adapted to bear. An arm 50 integrally connected to the arm 5| is provided for adjusting the position 01 the thermostat 52 on the base to vary the temperature at which the thermostat will actuate the carriage 31.

The purpose of the tension spring 59 is to keep the carriage 31 and the arm 53 in engagement with the opposite ends of the connecting rod 59 so that on temperature variations the arm 53 will rock the carriage 31 back and forth about the knife edges l4 and I8, and carry with it the magnet 4|. The fiexibility of the strip 2| will permit the magnet 23 to follow the magnet 4| thereby moving the resistance elements. The tube 1 is held stationary by means of the ring I5 and the mercury I9 is also held stationary by the depression |8 so that as the temperature to which the thermostat 52 is subjected determines the position of the arm 53 it will also determine the position of the horse shoe magnet 4|, the bar magnet 23, and the relative positions of the re sistance elements 25 and 25 and the globule of mercury |9.

This type of variable resistance has the advantage that the mercury has a fixed relation to its support so that the only sliding contact is between the mercury and the resistance elements. The resistance to movement therefore between the mercury and the resistance elements will be very slight so that the tendency for a jumpy action therebetween will be materially reduced. As a result the resistance to movement of the bimetallic element is also decreased so that its sensitivity is correspondingly increased.

The weight 46 may be adjusted on the screw threaded stem 45 until it is in a proper position to counterbalance the carriage 31 and magnet 4| as well as the arm 22, magnet 23, and resistance elements 25 and 26 as they are rotated by means of thermostat 52 as it responds to variations in temperature. The combined effect of the counterbslancing weight 48 and the mercury type of contactor is to so reduce the eiIort required to operate the control that a motion multiplying linkage may be used between the condition responsive element and the resistance element without materially affecting the sensitivity of the condition responsive element.

Referring now to the modification disclosed in 4 it will be seen that the open end of a glass tube is closed by means of a. flexible metal bellows 1| which is sealed thereto. The tube and bellows are fixedly supported by means of a link 12 which is suitably connected to the base 13 by some means (not shown). The lower end of the tube 10 is provided with an indentation 14 in which is fixedly supported a globule of mercury "it. The bellows 1| is provided with a cross pin 16 on which is pivotally mounted an arm 11 which extends through an aperture in the bellows 1| and is sealed thereto as indicated at 1|. The lower end of the arm 11 supports a resistance element 8|! in the form of a coiled wire. One end of the coiled wire is electrically connected to the arm 11 to which is connected in turn an external conductor 8|. Conductor 32 is connected to the other end of the resistance 30 and sealed through the glass tube as indicated at 33 and connected to external conductor 44. A conducting element is sealed into the tube 10 at the indentation 14 and extends within the globule 0t mercury 15 and at its other end is connected to the external conductor 85.

A portion 31 of the base 13 extends forwardly in the form of a shelf on which is seated one end of bellows 33, the. other end carrying a movable stem 8! which engages the lever 30 which in turn pivots about the knife edge 3| suitably connected to the base 13. The end of the lever 30 opposite the bellows 38 carries a projection 32 which centers one end of a compression spring 93, the other end of which seats about a centering cap 94 which is adiustably positioned by means of the screw 95 which may be screwed in and out w of the shelf 81 by means of the knurled head I. It will be seen that the compression spring 03 opposes rotation of the lever about the knife edge 9| by means of the bellows 33 and therefore adjustment of the screw which will varythe force exerted by the spring 33 will adjust the temperature or pressure at which the bellows II will rotate the lever 90. t

The lever 90 is integrally connected to an upstanding arm 98 which has at its upper end a forwardly extending portion "having a slot ll.

therein which engages the pin IOI on the outer endofthearm'l'l. Thereforeasthetubellis fixed by means of the supporting ring I! rotation of the lever ll by the bellows it will cause a back and forth movement of the portion is of the arm OI and a consequent rotation of the arm I'l about its pivot II and a movement of the resistance ll back and forth across the globule of mercury II which will vary the relative amounts of resistance in the external circuits to which the conductors ll, 84, and ll are connected.

This modification will have the advantages of the first modification also in that the globule of mercury remains fixed with respect to its support and has sliding engagement only with the resistance element ll.

Coming now to the modification disclosed in Figure the sealed glass tube III is identical with the tube ll of the first modification. This tube is supported by means of ring Hi integrally connected to the pin H2 shown in dotted lines which is pivotally mounted in the base ill to provide for rotation of the tube Ill. As in the other modifications the tube H0 is provided with an indentation Ill in which is fixedly mounted a globule-of mercury H5. A conductor ill is sealed through the tube at the indentation and has one end in electrical contact with the mercury III and the other end connected to an external conductor 8. A fiexible strip iil similar to that disclosed at II in the first modification is sealed into the upper end of the tube ill and at its lower end is suitably connected to an arm III which at its lower end carries a weight Ill and an insulating member I22 which supports the resistance element III formed by a coiled resistance wire. The strip H1 is very flexible so that under the influence of the weight III the arm I will tend to remain in a vertical position regardless of the pomtion of the tube Ill.

One end of the resistance III is connected by means of conductor It! to the arm I20 which through the element H1 is connected to external conductor I. The other end .of the resistance element III is connected to the conductor III which is sealed into the upper end of the glass tube III as indicated at J2! and is electrically connected to the external conductor I.

As in the second modification a portion of the base 8 is'bent forwardly to form a shelf Ill which supports a bellows ISI for operating a lever luabout a knife ed e I and which is opposed by the adjusting spring I in the same manner as described in the second modification. The force exerted by the spring I34 is adjusted by means of the adjusting screw Iii. The lever I82 is integrally connected to an upstanding arm I31 which has a forwardly extending portion III at its upper end having a slot ill therein. The ring Ill isconnectedtoanarm having apin Ill thereon which rides in the slot in so that as the lever II! is rocked back and forth by the bellows III the sides of slot I" will engage the pin I" and through the arm I rotate the tube lit back and forth about its pivot III and as the resistance I28 remains substantially stationary under the infiuence of the weight III and the fiexible support I H, the effect will be to move the mercury Ill back and forth along the resistance element I28 thereby varying the relative amount of resistance in the external circuits to which the conductors I20, Ill, and III are connected.

To thering Ill i integrally connected ascrew threaded stem m on which is adjustably positioned a counter-weight III for the purpose of counter-balancing the tube Ill so that the bellows Ill may be made more sensitive.

It is therefore seen that each of the three modifications has the advantage that the mercury remains in fixed relation to its support and has a sliding engagement only with its resistance element and as such engagement offers a comparatively small resistance to relative movement that the chances of a jumpy or uneven action is materially reduced.

It is pointed out that the tubes in each case may be evacuated and filled with hydrogen or other gas if desired. It is of course understood that the resistances and mercury are placed in a sealed tube for the purpose of preventing oxidation and corrosion of the resistance coils and themercury.

Certain changes and modifications in this invention may occur to those who are skilled in the art and it is therefore understood that we are to be limited only by the scope of the appended claims and not by the specific embodiments disclosed.

We claim as our invention:

1. In a device of the character described comprising in combination. a sealed enclosure, a globule of mercury, means at the bottom of said enclosure for fixedly mounting said mercury with respect to said enclosure, a resistance element. said resistance element being hung from the upper part of said enclosure by means of a resilient hinge member and in contact with said mercury, magnetic means carried by said resilient member, magnetic means outside of said enclosure for attracting said magnetic means within said enclosure. and means for moving said magnetic means outside of said enclosure to cause movement of said resistance element across said mercury.

2. In combination, a sealed tube. a globule of mercury, a relatively small indentation in the bottom of said tube, said mercury being carried in said indentation and extending slightly above the floor of the tube, a resistance element, means supporting said resistance element from the upper part of said tube for swinging movement in contact with the surface of said mercury, magnetic means mounted within said tube on said supporting means, a magnetic element outside of said tube for attracting said magnetic means, and a condition responsive element for moving said magnetic element back and forth in response to variations in the value of the condition.

3. In combination, a sealed tube, a globule of mercury, means for mounting said mercury at the bottom of said tube and in fixed relation to said tube. a resistance element, means supporting said ruistance element from the upper part of said tube for swinging movement in contact with said mercury, magnetic means mounted within said tube on said supporting means, a'magnetic element comprising a horse shoe magnet located outside of and embracing the lower end of said tube, the two ends or said horse shoe being adjacent to and on oppodte sides of said magnetic means. and means for swinging said horse shoe magnet about substantially the same axis as that about which said resistance element swings.

4. In a device of the character described counprising in combination, a glass tube having an open end. an indentation in the other end, a

giobule of mercury in said indentation and extending slightly above it, a resistance element, a flexible bellows sealing the open end of said i tube; a support for said resistance element extending through said bellows and sealed with respect thereto, said support holding said resistance element in contact with said mercury, and a condition responsive device outside of said tube and bellows engaging said support to cause said resistanceelement to move back and forth across said mercury on variations in the value of the condition towhich said device responds.

5. In a device of the character described comprising in combination, a glass ,tubehaving an open end, an indentation in the other end, a globule of mercury in said indentation and extending slightly above it, a resistance element, a flexible bellows sealing the open end of said tube; a support for said resistance element pivoted inside of the enclosure formed by said tube and bellows and extending through said bellows and sealed with respect thereto, said support holding said resistance element in contact with said mercury, and a condition responsive device outside of said tube and bellows engaging said support to cause it to rotate about its pivot and move said resistance element across said mercury.

6. In combination, a pivotally mounted sealed tube, means at the bottom of the tube for supporting a globule of mercury in fixed relation to the tube, a globule of mercury supported therein, a resistance element, an arm carrying said resistance element, resilient means supporting said arm from the upper portion of said tube so that said resistance element is free to swing with respect to saidtube back and forth across said mercury, a weight on said arm so that it will normally hang vertically, and means for rocking said tube back and forth to move said mercury across said resistance as said resistance remains substantially stationary.

'1. In a device of the character described comprising in combination, a base, a carriage pivotally mounted on said base, a sealed glass tube supported on said carriage, an indentation in the bottom of said tube, a globule of mercury supported in said indentation, a resistance element, an arm carrying said resistance element, a flexible element suspending said am from the top of said tube whereby said resistance element can swing back and forth with respect to said tube across said mercury, a weight on said arm so that it will normally hang vertically, a condition responsive device for rotating said carriage about its pivot to move said mercury across said resistance element while said resistance element remains substantially stationary, and an adjustable weight on said carriage above its pivot for properly counterbalancing said carriage and tube.

8. In a device of the character described, comprising in combination, a sealed container, a globule of mercury, means at the bottom of said tube for supporting said mercury in fixed relation to said tube, a resistance element, means supporting said resistance element within said tube and in contact with said mercury, weighted means holding said resistance element substantially stationary, and condition responsive means moving said mercury back and forth across saidresistance element.

9. In a device of the character described, a hermetically sealed tube, a relatively small indentation in the floor of said tube, a globule of mercury carried in said indentation, an elongated resistance element, a member carrying said resistance element, said member being sealed within said tube by laterally flexible means and movable with respect thereto. said resistance being held in a position so as to contact the surface of said globule of mercury, relative movement between said member and said tube causing a longitudinal movement of said resistance element with respect to said mercury, and means outside said tube for causing relative movement. between said member and tube.

10.In a resistance device the combination of, an hermetically sealed casing having a relatively small indentation in the floor thereof, a globule of mercury in said indentation and extending slightly above the floor of said casing, a resistor slidable over the surface of said mercury, osciliatable mounting means for said resistor, laterally flexile means for sealing said mounting means to said casing, and condition responsive means for oscillating said mounting means to vary the effective resistance of said device.

11. In a resistance device the combination of, an hermetically sealed casing having a relatively small indentation in the floor thereof, a globule of mercury in said indentation and extending slightly above the floor of said casing, a resistor slidable over the surface of said mercury, oscillatable mounting means for said resistor, laterally flexile means for sealing said mounting means to said casing, and condition responsive means, including magnetic driving means, for oscillating said mounting means to vary the efiective resistance of said device.

12. In a resistance device the combination of, an hermetically sealed casing having a relatively small indentation in the floor thereof, a globule of mercury in said indentation and extending slightly above thefioor of said casing, a resistor slidable over the surface of said mercury, osclllatable mounting means for said resistor, laterally flexile means for sealing said mounting means to said casing, and condition responsive means for developing a force to produce relative movement between said mercury and said resistor to vary the effective resistance of said device,

13. In a resistance device the combination of, an hermetically sealed casing having a relatively small indentation in the floor thereof, a globule of mercury in said indentation and extending slightly above the floor of said casing, a resistor slidable over the surface of said mercury, oscillatable mounting means for said resistor, laterally fiexile means for sealing said mounting means to said casing, condition responsive means movable in accordance with variations in a variable condition, and connecting means between said condition responsive means and said mounting means.

14. In a resistance device the combination 01',-

GIFFORD I. HOLMES. ROBERT S. CRAIG. 

